In dry cleaning, a solvent absorbed in laundry during a cleaning process is removed by a drying process, and the solvent thereby vaporized is condensed and recovered in a liquid form. The condensed solvent obtained in this drying and recovering process contains water, which was originally retained in the laundry. This water needs to be separated from the solvent to recover a high-purity solvent free from the liquid. Such a process is also necessary if the dry-cleaning machine includes a distiller, such as the one disclosed in Patent Document 1, which is used to recycle the solvent that has been tainted during the laundry-cleaning process. The solvent collected from such a distiller also contains water, which must be separated from the solvent to recover a high-purity solvent. For this purpose, conventional dry-cleaning machines include a water separator. If the solvent is a commonly used conventional petroleum solvent, it is relatively easy to separate water from the solvent by a so-called relative density difference separation method, because there is a large difference between the relative density of water, which is 1, and that of the solvent, whose density is approximately 0.8.
In recent years, petroleum solvents used thus far are being replaced with silicone solvents because the latter is less harmful to the environment, the health of the dry-cleaning workers, and to the health of the owners of the cleaned laundry, who may suffer from a solvent remaining in the cleaned articles. The relative densities of silicone solvents are approximately 0.95 for cyclic silicone solvents and approximately 0.85 for straight-chain silicone solvents. Thus, the difference in relative density between the silicone solvents and water is smaller than that between the petroleum solvents and water. Though the silicone solvents can also be separated by the aforementioned separation method utilizing the difference in relative density, the separation process requires a longer period of time thus making the process difficult to be coordinated with the drying cycle of the machine. Accordingly, there is a demand for a new type of water separator capable of separating water from a silicone solvent whose relative density differs slightly from that of water while maintaining good coordination with the cyclic operation of the machine.
For solving this problem, the applicant has proposed a water separator, as disclosed in Patent Document 2. FIG. 7 is a schematic sectional view of this conventional water separator. This water separator uses a so-called coalescer-type liquid-liquid separation filter.
As shown in FIG. 7, the water separator includes a liquid storage tank 50 for holding a mixture of water and a condensed solvent, a substantially S-shaped drainage pipe 54 connected to the bottom of the tank 50, and an air pipe 55 connecting the horizontal section 54b of the drainage pipe 54 and the top of the tank 50. The liquid storage tank 50 contains a cylindrical filter 58 consisting of a micro-fiber non-woven fabric held by a holder 59. Inside this filter, a solvent recovery pipe 60 penetrating through the bottom of the tank 50 has its upper end port 60a open in the upper direction.
During the drying and recovering operation, warm air is emitted from the drum with a vaporized solvent and steam, and this air is rapidly cooled by a cooler to condense the vaporized solvent and steam into a liquid mixture, i.e. a solvent in which water is mixed. The liquid mixture flows through a liquid mixture line 51 into the tank 50 and is collected. The solvent contained in the liquid mixture passes through the fiber mesh of the filter 58, whereas the water is trapped onto the fiber surface and condensed into large drops of water. Then, due to their weight (or relative density difference from that of the solvent), the drops of water settle and gather at the bottom of the tank 50. With the increase in the level of the liquid mixture (or the level of the low-purity solvent in the upper layer), the solvent level within the filter chamber surrounded by the filter 58 also increases. The solvent will then reach the upper end port 60a, flow into the solvent recovery pipe 60 and is extracted from the water separator.
Meanwhile, the water collected in the lower layer of the tank 50 is pushed up into the vertical section 54a of the drainage pipe 54. The water level is constantly lower by L than the level of the solvent in the upper layer, due to the difference in relative density between the water and the solvent. With an increase in the solvent level within the upper layer of the tank 50, the water level within the vertical section 54a of the drainage pipe 54 also increases. The water will finally reach the horizontal section 54b of the drainage pipe 54 and flow to the outside.
Thus, the water flows out from the drainage pipe 54, while the solvent returns through the solvent recovery pipe 60 to a liquid supply tank. Normally, the rate of separating the two liquids by the filter 58 is adequately higher than the inlet velocity of the liquid mixture. Therefore, the water and the solvent are surely separated according to the inflow of the liquid mixture, so that the tank 50 will not be filled. The air pipe 55 prevents the water from being siphoned through the drainage pipe 54. If the water level in the drainage pipe 54 falls below the horizontal section 54b according to a decrease in the level of the solvent in the upper layer of the tank 50, the water flow through the drainage pipe 54 will immediately stop.
Silicone solvents are water-repellent and do not mix with water. Therefore, it is basically possible to separate water from the silicone solvent by the previously described device. However, the aforementioned conventional water separator has the following problem:
During the drying and recovering operation, a fan is activated to forcefully produce a circulation of air through a passage consisting of the drum, the heater for heating the air, the cooler for condensing the solvent, and other structural elements. Normally, its wind pressure is so high as to cause highly pressurized air to flow into the liquid mixture line 51 along with the liquid mixture. This air flows into the tank 50 and increases the pressure within the top space of the tank 50. As shown in FIG. 7, within the tank 50, the low-purity solvent having a relatively high water content is located over the water, with an interface separating the two liquids. If the aforementioned high-pressure current of air rushes into the tank 50, the wind pressure pushes the liquid surface and lowers the aforementioned interface. The wind pressure is significantly machine-specific since it greatly depends on the air-tightness of the air-circulation passage during the drying and recovering operation. It may also vary according to the amount and/or stirred state of the laundry contained in the drum. Therefore, in the conventional dry-cleaning machine, the interface between the solvent and water within the tank 50 is unstable and makes a vertical motion with a considerable magnitude.
This vertical motion of the interface causes the following problem: During the cleaning process, if dust, fine lint and other unwanted matter come off the laundry and are collected with the solvent, much of this matter gather around the interface due to their relative densities. If the interface rises to a level as high as the filter 58, the unwanted matter gathering around the interface will stick to the filter 58, clogging its mesh and thereby impeding the solvent from passing through it. In the worst case, the rate of separating the two liquids by the filter 58 will be lower than the inlet velocity of the liquid mixture flowing into the tank 50. In this case, the tank 50 will be overfilled or, minimally, the user will need to clean or replace the filter 58 more frequently. Furthermore, in the aforementioned situation, the liquid pressure on the filter 58 can be so high as to help the water pass through the filter 58 with the solvent. If this occurs, the recovered solvent will contain the water and be unusable.
If the interface comes to too low a level, the solvent will flow through the drainage pipe 54 to the outside. Silicone solvents are far more expensive than petroleum solvents. Therefore, allowing this outflow of the silicone solvent will increase the running costs of the dry-cleaning machine. Moreover, the unwanted matter present around the interface can clog the drainage pipe 54, impede or, in the worst case, completely stop the water drainage. If this occurs, the tank 50 will be filled, allowing the overflow of the liquids from the tank 50 or the mixture of water into the solvent, as in the case of the clogging of the filter 58.
In some cases, particularly if the silicone solvent is used, the solvent collected through the solvent recovery pipe 60 by the previous dry-cleaning machine may contain a considerably high percentage of water. The reason is as follows:
When the vaporized solvent contained in the air emitted from the drum is cooled and condensed into a liquid form, the water mixed in the solvent normally turns into large particles, i.e. water drops. However, occasionally, colloidal particles consisting of fine water particles covered with the solvent may be formed. Particularly, silicone solvents are easier to form such colloidal particles; the liquid mixture of the solvent and water recovered from the drying air passage often takes the form of an emulsion in which a large number of colloidal particles are dispersed. Similarly, the solvent distiller vaporizes the solvent by heating and then condenses it into a liquid form by cooling. Therefore, the solvent taken out from the distiller often takes the form of an emulsion in which water is dispersed in the form of colloidal particles.
The colloidal particles have various diameters. Large particles will be stopped by the filter 58 and finally separated by the relative density separation method. However, there are many fine colloidal particles whose diameter is as small as 1 μm. These fine colloidal particles can easily pass through the mesh of the filter 58, so that the silicone solvent thereby recovered will have water mixed in it.
The water-containing solvent thus recovered can cause various problems: Using this solvent in the next cleaning cycle may cause shrinkage of the laundry articles or damage their fabrics. The laundry articles may be harder to dry and easier to gather mold due to inadequate dryness while they are stored. The solvent itself can also suffer from growth of bacteria and give off a smelly stench. Such a solvent is no longer usable for cleaning and must be disposed of. As pointed out earlier, silicone solvents are considerably expensive compared to petroleum solvents. If they cannot be recycled, cleaning will be very costly.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. H07-289788
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2004-121644